frontswap: get rid of swap_lock dependency
Minchan Kim [Tue, 30 Apr 2013 22:26:54 +0000 (15:26 -0700)]
Frontswap initialization routine depends on swap_lock, which want to be
atomic about frontswap's first appearance.  IOW, frontswap is not present
and will fail all calls OR frontswap is fully functional but if new
swap_info_struct isn't registered by enable_swap_info, swap subsystem
doesn't start I/O so there is no race between init procedure and page I/O
working on frontswap.

So let's remove unnecessary swap_lock dependency.

Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
[v1: Rebased on my branch, reworked to work with backends loading late]
[v2: Added a check for !map]
[v3: Made the invalidate path follow the init path]
[v4: Address comments by Wanpeng Li <liwanp@linux.vnet.ibm.com>]
Signed-off-by: Konrad Rzeszutek Wilk <konrad@darnok.org>
Signed-off-by: Bob Liu <lliubbo@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andor Daam <andor.daam@googlemail.com>
Cc: Florian Schmaus <fschmaus@gmail.com>
Cc: Stefan Hengelein <ilendir@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/frontswap.h
mm/frontswap.c
mm/swapfile.c

index 6c49e1e..8293262 100644 (file)
@@ -23,7 +23,7 @@ extern void frontswap_writethrough(bool);
 extern void frontswap_tmem_exclusive_gets(bool);
 
 extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
-extern void __frontswap_init(unsigned type);
+extern void __frontswap_init(unsigned type, unsigned long *map);
 extern int __frontswap_store(struct page *page);
 extern int __frontswap_load(struct page *page);
 extern void __frontswap_invalidate_page(unsigned, pgoff_t);
@@ -98,10 +98,10 @@ static inline void frontswap_invalidate_area(unsigned type)
                __frontswap_invalidate_area(type);
 }
 
-static inline void frontswap_init(unsigned type)
+static inline void frontswap_init(unsigned type, unsigned long *map)
 {
        if (frontswap_enabled)
-               __frontswap_init(type);
+               __frontswap_init(type, map);
 }
 
 #endif /* _LINUX_FRONTSWAP_H */
index 2760b0f..538367e 100644 (file)
@@ -121,8 +121,13 @@ struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
        int i;
 
        for (i = 0; i < MAX_SWAPFILES; i++) {
-               if (test_and_clear_bit(i, need_init))
+               if (test_and_clear_bit(i, need_init)) {
+                       struct swap_info_struct *sis = swap_info[i];
+                       /* __frontswap_init _should_ have set it! */
+                       if (!sis->frontswap_map)
+                               return ERR_PTR(-EINVAL);
                        ops->init(i);
+               }
        }
        /*
         * We MUST have frontswap_ops set _after_ the frontswap_init's
@@ -156,20 +161,30 @@ EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
 /*
  * Called when a swap device is swapon'd.
  */
-void __frontswap_init(unsigned type)
+void __frontswap_init(unsigned type, unsigned long *map)
 {
        struct swap_info_struct *sis = swap_info[type];
 
-       if (frontswap_ops) {
-               BUG_ON(sis == NULL);
-               if (sis->frontswap_map == NULL)
-                       return;
+       BUG_ON(sis == NULL);
+
+       /*
+        * p->frontswap is a bitmap that we MUST have to figure out which page
+        * has gone in frontswap. Without it there is no point of continuing.
+        */
+       if (WARN_ON(!map))
+               return;
+       /*
+        * Irregardless of whether the frontswap backend has been loaded
+        * before this function or it will be later, we _MUST_ have the
+        * p->frontswap set to something valid to work properly.
+        */
+       frontswap_map_set(sis, map);
+       if (frontswap_ops)
                frontswap_ops->init(type);
-       } else {
+       else {
                BUG_ON(type > MAX_SWAPFILES);
                set_bit(type, need_init);
        }
-
 }
 EXPORT_SYMBOL(__frontswap_init);
 
index d417efd..6c340d9 100644 (file)
@@ -1509,8 +1509,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 }
 
 static void _enable_swap_info(struct swap_info_struct *p, int prio,
-                               unsigned char *swap_map,
-                               unsigned long *frontswap_map)
+                               unsigned char *swap_map)
 {
        int i, prev;
 
@@ -1519,7 +1518,6 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio,
        else
                p->prio = --least_priority;
        p->swap_map = swap_map;
-       frontswap_map_set(p, frontswap_map);
        p->flags |= SWP_WRITEOK;
        atomic_long_add(p->pages, &nr_swap_pages);
        total_swap_pages += p->pages;
@@ -1542,10 +1540,10 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
                                unsigned char *swap_map,
                                unsigned long *frontswap_map)
 {
+       frontswap_init(p->type, frontswap_map);
        spin_lock(&swap_lock);
        spin_lock(&p->lock);
-       _enable_swap_info(p, prio, swap_map, frontswap_map);
-       frontswap_init(p->type);
+        _enable_swap_info(p, prio, swap_map);
        spin_unlock(&p->lock);
        spin_unlock(&swap_lock);
 }
@@ -1554,7 +1552,7 @@ static void reinsert_swap_info(struct swap_info_struct *p)
 {
        spin_lock(&swap_lock);
        spin_lock(&p->lock);
-       _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
+       _enable_swap_info(p, p->prio, p->swap_map);
        spin_unlock(&p->lock);
        spin_unlock(&swap_lock);
 }
@@ -1563,6 +1561,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
        struct swap_info_struct *p = NULL;
        unsigned char *swap_map;
+       unsigned long *frontswap_map;
        struct file *swap_file, *victim;
        struct address_space *mapping;
        struct inode *inode;
@@ -1662,12 +1661,14 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
        swap_map = p->swap_map;
        p->swap_map = NULL;
        p->flags = 0;
-       frontswap_invalidate_area(type);
+       frontswap_map = frontswap_map_get(p);
+       frontswap_map_set(p, NULL);
        spin_unlock(&p->lock);
        spin_unlock(&swap_lock);
+       frontswap_invalidate_area(type);
        mutex_unlock(&swapon_mutex);
        vfree(swap_map);
-       vfree(frontswap_map_get(p));
+       vfree(frontswap_map);
        /* Destroy swap account informatin */
        swap_cgroup_swapoff(type);